A thermal radiation detector operates by converting incident radiation into heat. The radiation is absorbed by a structure, typically a metal film, and causes the temperature of the sensor to increase. This temperature change is measured by means of a variety of physical effects. Examples include temperature-dependent electric resistivity in bolometers, gas pressure in Golay cells, the Seebeck effect in thermopiles, and the pyroelectric effect in pyroelectric sensors. In all of these cases, it is desirable that the metallic absorber have high efficiency across the largest possible range of wavelengths and a low thermal mass. Existing solutions include detector architectures that incorporate (a) metal-black coatings, (b) thin metal coatings, and (c) quarter-wavelength (QW) spacer/absorber structures. Type (a) detectors are typically very fragile, type (b) detectors typically require very specific metal films due to the high-reflectivity properties of metals, and type (c) detectors are typically very efficient (approaching 100% absorption) at very specific wavelength bands, where the given QW spacer/absorber structure is most efficient. The latter type of detector has anti-nodes, making it inefficient at certain wavelengths within the absorption band of the metal film. The fabrication of type (c) detectors can be complicated, as metal and dielectric coatings have to be produced in different chambers for contamination reasons, and the QW spacer/absorber structures can be single or multi-layered dielectric structures of considerable complexity.
Thus, what is still needed in the art is an improved optical detector that operates efficiently over a wide wavelength range and that is simple to manufacture. Advantageously, the optical detector would permit the use of metal films that have previously been restricted due to their high-Fresnel reflection losses.